For the purpose of increasing an efficiency of an internal combustion engine while reducing the concentration of harmful materials contained within exhaustion gas, it is necessary to measure a mass of intake-air sucked into the internal combustion engine, accurately, thereby controlling a mass of fuel injection, so that the air-fuel ratio can be kept at a target air-fuel ratio, which is determined by the operating condition thereof. Thus, the present invention relates to a technology for measuring a mass of air taken into the internal combustion engine, correctly.
Conventionally, as is described in Japanese Patent Laying-Open No. Hei 7-301144 (1995), for example, an apparatus for measuring a mass of air sucked into the internal combustion engine, comprises:                a rotation speed detection means for detecting the rotation speed of a crank shaft;        an intake pressure detection means for detecting the intake-air pressure within an intake manifold;        a timing detection means for detecting the operation timing of a valve driving mechanism located at a side where the open/close timing thereof is adjusted by means of an open/close timing means of a variable intake valve;        a charging efficiency calculation means for calculating a charging efficiency, i.e., a ratio between an actual weight of an intake-air introduced into a cylinder and a weight of an intake-air introduced into the cylinder under a predetermined condition of the atmosphere, or a correlation value thereof correlating to that charging efficiency, upon the basis of at least the rotation speed detected by said rotation speed detection means, the intake pressure detected by said intake pressure detection means and the operation timing detected by said timing detection means; and        an intake-air mass calculation means for obtaining a mass of intake-air introduced into the cylinder, upon the basis of the charging efficiency or the correlation value thereof, which is calculated out by the charging efficiency calculation means, and also the intake-air pressure detected by the intake pressure detection means, thereby measuring the mass of intake-air introduced into the cylinder of the internal combustion engine.        
In the conventional art mentioned above, however when calculating the charging efficiency upon the rotation speed, the intake-air pressure and the operation timing of the variable intake valve, i.e., the opening/closing timing thereof, a three-dimension (3D) map is used therein, having variables; such as, the rotation speed, the intake-air pressure and the operation timing of opening/closing the variable intake valve. For example, if trying to make up the map by dividing the variable region or domain of the operation timing for opening/closing the variable intake valve into ten (10) regions, respectively, then the map comes up to be 10×10×10×1,000 times large in memory size thereof; therefore, man-hour of collecting data through an actual machine comes to be massive, for making up that map, and also for a ROM for memorizing the map therein, it must be large in the memorizing capacity thereof. Accordingly, it rises up a manufacturing cost of such an engine controller apparatus (ECU).